DHCP also update Dynamic DNS for static leases

Previously, Dynamic DNS is only updated for clients that get addresses from the DHCP address pool. Static mappings are ignored.

Adding this line updates Dynamic DNS for both static-mapped and dynamic DHCP clients.
Typo in configuration option

Should be 'leases', not 'mappings'.
Merge pull request #699 from evansus/patch-2

DHCP also update Dynamic DNS for static leases